The invention relates to an adjustment device for adjusting the relative rotational angle position of a camshaft relative to a crankshaft of an internal combustion engine with an adjustment transmission that is constructed as a triple-shaft transmission and that has a crankshaft-fixed drive part, a camshaft-fixed driven part, and an adjustment shaft connected to an adjustment motor shaft of an adjustment motor.
To guarantee a reliable start of an internal combustion engine with a hydraulic or electric camshaft adjustment system, the camshaft must be located in the so-called base or emergency running position. For intake camshafts, this position typically lies in a “retarded” position; for exhaust camshafts, it lies in an “advanced” position. In normal operation of the vehicle, the camshaft is moved into the respective base position and fixed or locked there when the engine is turned off.
Conventional, hydraulically activated rotary piston adjusters, such as vane cells, pivoting or segmented blades, have a locking unit. This unit fixes the hydraulic adjuster in its base position until sufficient oil pressure has built up for adjusting the camshaft. If the engine stalls, the camshaft can be located in an undefined position outside of the base position.
For hydraulic camshaft adjustment systems with a “retarded” base position, the camshaft is automatically moved into the retarded base position at the next start of the internal combustion engine and when there is insufficient oil pressure due to the camshaft moment of friction, which acts against the camshaft direction of rotation. If the system has an “advanced” base position, the camshaft must be moved into the advanced base position when there is insufficient oil pressure against the camshaft moment of friction. This happens mostly with the help of a compensation spring, which generates a moment directed against the camshaft moment of friction.
These methods, which are typical for hydraulic camshaft adjusters, for moving into the base position after the internal combustion engine stalls cannot be used in electrically driven camshaft adjusters. They are also unnecessary as long as the adjustment motor system is intact and the camshaft can be moved into the respective base position also for vertical internal combustion engines or for a new start. For electrical adjustment motor systems, however, the adjustment motor and/or its controller can be eliminated and therefore reaching the base position can fail.
In DE 41 10 195 A1, a device for adjusting the rotational angle position between a camshaft and a crankshaft of an internal combustion engine is described, with an adjustment mechanism, which is constructed as a triple-shaft transmission and which has a drive shaft connected to the crankshaft, a driven shaft connected to the camshaft, and an adjustment shaft connected to an electric adjustment motor, wherein for a stationary adjustment shaft there is a stationary transmission ratio I0, which defines the type of transmission (minus or plus transmission) and the adjustment direction of the camshaft to the base or emergency running position.
Each adjustment device has the goal of smooth running and precise setting of the camshaft position. So that the function of the internal combustion engine can be maintained at least temporarily if the adjustment motor system becomes disabled, the adjustment angle is limited. In such a case, however, there is no indication on reaching the base or emergency running position. In addition, for each construction, the base position must be located in one of the two end positions of the camshaft adjuster; the camshaft adjuster always runs towards advanced or retarded contact.
Under certain thermodynamic viewpoints, however, it is desirable to select an arbitrary middle position as the base position.